Crystal formation reduction in lubricating compositions

ABSTRACT

Lubricating oil formulations comprising base oil, sulfur-phosphorous anti-wear/extreme pressure agent and hindered phenol antioxidant, which combination of extreme pressure agent and hindered phenol antioxidant produces crystals and containing antioxidants, wherein the base oil is characterized as having a saturates content of 99 wt % or more is stabilized against crystal formation by the addition of a minor amount of high molecular weigh di- or polycarboxylic acid, or anhydride and an ester.

This invention relates to lubricating oil based on base stocks having asaturates content of 99 wt % or more, preferably essentially 100%saturates and containing sulfur-phosphorus containing anti-wear/extremepressure additives and hindered phenol antioxidants which combination ofanti-wear/extreme pressure agent and hindered phenol antioxidant areprone to crystal formation, wherein the formation of crystals is reducedor eliminated by the use of a crystallization suppressant.

Lubricating oils containing various antioxidants or esters or fatty acidamides or sulfur-phosphorus additives in combination with phenols areknown in the literature.

U.S. Pat. No. 5,167,844 is directed to a formulation comprising a baseoil, at least one sulfur phosphorus containing compound, at least oneamine and at least one hindered phenol.

JP 07034078 is directed to a hydraulic oil comprising mineral oil withan aromatic content of up to 1.5 wt % and a phenolic and aminicanti-oxidant, an alkenyl succinic acid imide rust inhibitor and aphosphoric acid type anti wear agent.

U.S. Pat. No. 5,590,483 is directed for lubricating a refrigerationsystem compressor using a break-in lubricating oil which is an estertype oil. Additionally an adipate, phthalate, azelate, sebacate,corrosion inhibitors such as alkali and/or alkaline earth metalsulfonate, antioxidants such as aminic or phenolic antioxidants andmetal deactivators such as triazoles.

WO 97/14776 is directed to hydraulic oils comprising base oils combinedwith an amine antioxidant, a phenolic antioxidant, a phosphate ester anda fatty acid amide and/or polyhydric alcohol ester.

U.S. Pat. No. 5,773,393 is directed to a composition comprising at least70 wt % oil of lubricating viscosity and an amount effective to inhibitmetal corrosion of a soluble additive comprising (a) at least one amidecompound of a mono- or polycarboxylic acid or reactive derivativethereof and (b) at least 0.5 equivalents of at least one primary orsecondary amine per mole of amide provided that when (a) is an amide ofa dicarboxylic acid and the amine is an alkanol amine the mixturecontains more than 0.5 equivalent of the amine (b) per equivalent of theamide.

The present invention is directed to a lubricating oil formulationhaving a reduced potential for the formation of crystals comprising amajor amount of a lubricating oil base stock having a saturates contentof 99 wt % or more, preferably essentially about 100 wt % and a minoramount of additives comprising a mixture of sulfur-phosphorus containinganti-wear/extreme pressure additive, hindered phenol antioxidant, and adi- or polycarboxylic acid, anhydride or mixture thereof and an ester,and to a method for reducing crystal formation in lubricating oilformulations comprising base oil having saturates content of 99 wt % ormore, preferably essentially about 100 wt %, and containing sulfurphosphorus anti-wear/extreme pressure additive and hindered phenolicanti-oxidant wherein the crystals are attributable to the interactionbetween the sulfur-phosphorus containing anti-wear/extreme pressureagent and the hindered phenol, by adding to said lubricating oil a minoreffective amount of di- or polycarboxylic acid, anhydride or mixturethereof and an ester.

The lubricating base oil is any oil of lubricating oil viscosity havinga saturates content of 99 wt % or more, preferably essentially 100 wt %.

Lubricating oils meeting this criterion are any natural mineral orpetroleum based lubricating oils derived from crude oil, tar sands,shale oil, etc., such that they have a saturates content in the recitedrange, or a mixture of natural mineral or petroleum based lubricatingoils in combination with poly-alpha olefins, isormerized wax orisomerized Fischer-Tropsch wax, the combination or mixture of such oilsbeing characterized as having a saturates content of 99 wt % or more,preferably essentially 100 wt %. Saturates content, for the purpose ofthis invention, is a measure of the absence of aromatic species, and wasdetermined using high pressure liquid chromatography (HPLC) according tomethod IP 368, except where otherwise expressly indicated.

The lubricating oil base stocks useful in the present invention have thetypical lubricating oil viscosity, usually possessing kinematicviscosities in the range of about 1.5 to 500 mm²/s at 100° C.,preferably 5 to 120 mm²/s at 100° C.

Mineral or petroleum based lubricating oil base stocks can be derivedfrom paraffinic, naphthenic and mixed base crudes. Conventional refinerytechniques include distillation, solvent and/or catalytic dewaxing,solvent extraction, hydrofinishing, hydrocracking, vis breaking,deasphalting, etc. Preferred mineral or petroleum based base stocksinclude white oils, hydrocracked or hydroisomerised base stocks.

Synthetic lubricating oils that can be used include esters of di- andtri-basic acids, reacted with linear or branched aliphatic alcohols suchas C₆-C₁₅ alcohols, such as di-2-ethylhexyl sebacate, phthalates, estersof glycols such as C₁₃ oxo acid diester or tetraethylene glycol, orcomplex esters such as one formed from 1 mole of sebacic acid and 2moles of tetraethylene glycol and 2 moles of 2-ethylhexanoic acid. Othersynthetic oils that can be used include silicone oils, e.g., methylpolysiloxanes, etc.; polyglycol oils, e.g., those obtained by condensingbutyl alcohol with propylene oxide; carbonate esters, e.g., the productof reacting C₆ oxo alcohol with ethyl carbonate to form a half esterfollowed by reaction of the latter with tetraethylene glycol, etc. Theonly requirement is that such oils be 100% saturated (that is, containno unsaturation).

Other suitable oils are the polyol ester oils made by reacting analiphatic polyol with carboxylic acid. Aliphatic polyols contain from 4to 15 carbon atoms and has from 2 to 8 esterifiable hydroxyl groups.Examples of polyols are trimethylolpropane, pentaerythritol,dipentaerythritol, neopentyl glycol, tripentaerythritol and mixturesthereof. The carboxylic acid reactant is selected from aliphaticmoncarboxylic acid or mixtures of aliphatic mono carboxylic acids ormixtures of aliphatic mono- and di-carboxylic acids. The carboxylicacids contain 4 to 12 carbons and include straight and branched chaincarboxylic acids.

Included in the group of synthetic oils are those recovered from tarsands, shale oil, light hydrocarbons produced via, for example, theFischer-Tropsch process for converting synthesis gas (CO and hydrogen)into hydrocarbons, wax isomerate oils produced by the catalytichydroisomerization of natural petroleum waxes (i.e., slack wax) orsynthetic waxes (i.e., Fischer-Tropsch waxes) or mixtures of such waxes.See U.S. Pat. No. 5,059,299 and U.S. Pat. No. 5,158,671 for descriptionof wax isomerization and the oils produced thereby. Other synthetic oilsinclude the polyolefins such as polybutene, polyisobutenes andespecially the polyalphaolefins, i.e., fluids formed by theoligomerzation of at least one 1-alkane hydrocarbon having from 6 to 20carbons, preferable 8 to 16 carbons, more preferably 8 to 12 carbons.

Regardless of the source of the oil, for the purposes of the presentinvention the lube oil base stock, be it a single oil or a mixture ofoils, is characterized as having a saturates content of 99 wt % or more,preferably about 99.8 wt % or more.

Sulfur-phosphorus containing anti wear/extreme pressure additives arewell known in the industry, and are materials containing both sulfur andphosphorus in the same materials. For the purposes of the presentspecification and appended claims, sulfur-phosphorus containinganti-wear/extreme pressure additives are those which react with hinderedphenol antioxidant to produce crystals. Those skilled in the formulationart can readily determine without expenditure of significant orinventive effort, whether a particular sulfur-phosphorus containinganti-wear/extreme pressure agent reacts with hindered phenol antioxidantto produce crystals. If it does not, it is not within the scope of thisinvention. Any sulfur-phosphorus containing anti-wear/extreme pressureagent which is found to react with hindered phenol antioxidant toproduce crystals in the subject base oil is within the invention andformulations containing such agent(s) and phenolic antioxidant will bebeneficially affected as evidenced by reduction or elimination ofcrystal formation by the addition of the high molecular weight di- orpolycarboxylic acid, anhydride or mixtures thereof and ester, as shownbelow, provided such carboxylic acid, anhydride or mixture thereof isused in an amount of at least about 0.0013 wt % for each 1 ppmphosphorus attributable to the sulfur-phosphorus containinganti-wear/extreme pressure agent, about 0.033 wt % or more ester is usedfor each 1 ppm phosphorus and the high molecular weight di- or polycarboxylic acid, anhydride or mixture thereof and the ester is employedin an ester to acid ratio of 25:1 by weight or higher.

Sulfur-phosphorus anti wear/extreme pressure additives are exemplifiedby, but not limited to, materials of the type:

wherein R₁, R₂ and R₃ are independently hydrogen or hydrocarbyl providedat least one is hydrocarbyl so as to render the material oil soluble andX is sulfur.

The hydrocarbyl groups preferably contain form 1 to 40 carbons and arearomatic and/or aliphatic groups and include aryl, alkyl and alkaryl andaralkyl and heteroatom substituted aromatic and aliphatic group, thehetero atom substitutents being sulfur, nitrogen or oxygen substitutedas such into the hydrocarbon selection or as sulfur, oxygen or nitrogencontaining moiety, e.g., —OR_(y), —SH, —SO₂H, —N(R_(y))₂,—C—R_(x)OR_(y),

etc., and mixtures thereof substituted onto or into the hydrocarbonbackbone, wherein R_(x) is C₁-C₂₀ hydrocarbyl or hydrocarbylene groupand R_(y) is hydrogen or a C₁-C₂₀ hydrocarbyl or hydrocarbylene group.

Such sulfur-organo phosphorus containing anti wear/extreme pressureagent is typically used at a concentration of from about 2 ppm to 320ppm phosphorus, preferably about 40 ppm to 200 ppm phosphorus, mostpreferably about 80 ppm to 130 ppm phosphorus.

An example of a sulfur phosphorus anti-wear/extreme pressure additivewhich has been found to react with hindered phenols to form crystals isa material is 2-ethylhexyl 10-ethyl-4-[[2-[(2ethylhexyl)-oxyl]-2-oxoethyl] thio]-7-oxo-8-oxa-3,5-dithia-4-phosphatetradecanoate, CAS #83547-95-9. Based on the name and the CAS number,it is believed this material has the following structure:

It must be noted that for the purposes of the present invention metaldihydrocarbyl dithio phosphates (metal DDP) or ashless DDP do not fallwithin the scope of the above definition of sulfur-phosphorus containinganti-wear/extreme pressure agents because it has been found that they donot form crystals when combined with hindered henols in base oils.

Hindered phenolic antioxidants are also quell known in the industry.Such materials include by way of example and not limitation2,6-di-t-butyl phenol, 2,6-di-t-butyl alkylated phenol where the alkylsubstituent is hydrocarbyl and contains between 1 and 20 carbon atoms,such as 2,6-di-t-butyl-4-methyl phenol, 2,6-di-t-butyl-4-ethyl phenol,etc., or 2,6-di-t-butyl-4-alkoxy phenol where the alkoxy substituentcontains between 1 and 20 carbons such as2,6-di-t-butyl-4-methoxyphenol; materials of the formula

where X is zero to 5, R₈ and R₉ are the same or different and are C₁-C₂₀hydrocarbyl which may contain oxygen or sulfur or be substituted withoxygen or sulfur containing groups; and materials of the formula

where y is 1 to 4 and R₁₀ is a C₁ to C₂₀ hydrocarbyl which may containoxygen, sulfur or nitrogen or be substituted with oxygen, sulfur ornitrogen containing groups, such as 2,6 di tert butyl dimethyl aminop-cresol,

wherein it is believed R₁₁ is C₈C₁₇ (CAS #125643-61-0), and mixtures ofsuch phenolic type antioxidants.

Preferably the phenolic antioxidant contains an ester group, such as informula IV above.

Phenolic type antioxidants are typically used at a concentration of fromabout 0.01 to 2.0 wt %, preferably 0.1 to 1.0 wt %, most preferably 0.3to 0.5 wt %, based on active ingredient.

In order to prevent or at least minimize the formation of crystals inlubricating oils based on base stock having 99 wt % or more saturatesand containing a mixture of sulfur-organo phosphorus anti-wear/extremepressure additive and phenolic antioxidant, wherein thesulfur-phosphorus containing anti-wear/extreme pressure agent is onewhich interacts with hindered phenol to produce crystals, a minor,crystal preventing effective amount of a high molecular weightcarboxylic acid, anhydride or mixture thereof is added to thelubricating oil formulation, in combination with an ester. In thoseinstances in which the 99 wt % or more saturates content oil alreadycontains esters in an amount sufficient to satisfy the ester contentrange stated later in this specification it may be sufficient simply toadd the aforesaid high molecular weight carboxylic acid, anhydride ormixture thereof which will be discussed in greater detail below.

The carboxylic acid anhydride or mixture thereof can be any highmolecular weight acid di-, or polycarboxylic acid anhydride or mixturethereof of molecular weight of about 300 to 5000. Such acids, anhydridesor mixtures thereof include polyhydrocarbylene substituted di- orpolycarboxylic acids wherein the poly hydrocarbylene group has amolecular weight in the range 300 to 5000, preferably 750 to 2000, mostpreferably 900 to 1000 (e.g., polyisobutylene) and wherein thecarboxylic group is preferably succinic or maleic acid, anhydride ormixture thereof.

Poly hydrocarbylenes are homopolymer or interpolymers of polymerizableolefin group containing monomers having from 2 to 16 carbons.Interpolymers are those made using two or more different olefinic groupscontaining monomer including monomer such as styrenes.Polyhydrocarbylene homo and interpolymers are well known in theliterature and to those skilled in the art and need not be furtherdescribed herein.

Preferably the carboxylic acid anhydride or mixture thereof used ispolyalkylene succinic or maleic acid, anhydride, or mixture thereof,most preferably polyisobutylene (PIB) succinic acid, anhydride ormixtures thereof wherein the PIB group has a molecular weight of about900 to 1000.

Such high molecular weight carboxylic acids, anhydrides or mixturesthereof are employed in an amount in the range of about 0.0026 to 0.8 wt%, preferably about 0.08 to 0.4 wt %, most preferably about 0.12 to 0.24wt %, based on active ingredients.

In general, from at least 0.0013 wt % of high molecule weight carboxylicacid, anhydride or mixture thereof is used for each 1 ppm from thesulfur-organo phosphorus anti wear/extreme pressure agent.

The ester can be any of the ester materials previously described assuitable synthetic oils. Esters such as phthalates and trimellitates canalso be used.

About 0.033 wt % or more ester is used for each 1 ppm phosphorus,preferably about 0.042 wt % or more ester is used for each 1 ppmphosphorus from the sulflur-organo phosphorus anti-wear/extreme pressureagent.

The crystal suppressing combination of high molecular weight acid and/oranhydride and ester is employed in an ester to acid ratio of 25:1 orhigher, preferably 32:1 or higher.

As previously stated, if the 99 wt % or more saturates content oil isitself a mixture of mineral oil or synthetic hydrocarbon oil, and ester,it may be enough merely to add a sufficient amount of high molecularweight acid/anhydride to the formulation to meet the aforesaid acid tosulfur-phosphorus anti-wear/extreme pressure additive ratio provided indoing so the ester/acid ratio also satisfies the 25:1 or morerelationship. If insufficient ester is present an amount of estersufficient to satisfy or reach the 25:1 or more ratio can be added tothe formulation in order to achieve crystal formation suppression.

EXAMPLES Example 1

This example (Table 1) is present to demonstrate the necessity of usingboth the high molecular weight carboxylic acid, anhydride or mixturethereof and an ester to suppress/eliminate the formation of crystals inoils of 99 wt % or more saturates content when using a mixture of sulfurphosphorus anti wear/extreme pressure agent and hindered phenolantioxidant. It is noteworthy that when the oil is of louver saturatescontent, the use of the high molecular weight carboxylic acid, anhydrideor mixture thereof by itself is sufficient to suppress/eliminate crystalformation, but that the use of an ester by itself in the same lowersaturates content oil is not sufficient to control crystal formation.Conversely in the case of 99 wt % or higher saturates content oil, thehigh molecular weight carboxylic acid, anhydride or mixture thereof byitself is not capable of controlling crystal formation.

TABLE 1 Crystals at 3 months Base oil (1) + 0.55 wt % S-P + 0.4 wt % +0.16 wt % No anti-wear/extreme hindered PIBSA (4) pressure agent (2)phenol (3) Base oil (5) + 0.55 wt % S-P + 0.4 wt % + 0.16 wt % Noanti-wear/extreme hindered PIBSA (4) pressure agent (2) phenol (3) Baseoil (6) + 0.55 wt % S-P + 0.4 wt % + 0.16 wt % Cloudy anti-wear/extremehindered PIBSA (4) pressure agent (2) phenol (3) Base oil (7) + 0.55 wt% S-P + 0.4 wt % + 0.16 wt % Cloudy anti-wear/extreme hindered PIBSA (4)pressure agent (2) phenol (3) Base oil (8) + 0.55 wt % S-P + 0.4 wt % +0.16 wt % Cloudy anti-wear/extreme hindered PIBSA (4) pressure agent (2)phenol (3) Base oil (9) (10) + 0.55 wt % S-P + 0.4 wt % + Esters (11)Yes anti-wear/extreme hindered pressure agent (2) phenol (3) Base oil(8) + 0.55 wt % S-P + 0.4 wt % + — Yes anti-wear/extreme hinderedpressure agent (2) phenol (3) Base oil (8) + 0.55 wt % S-P + 0.4 wt % +Ester (12) (3 wt %) Yes anti-wear/extreme hindered pressure agent (2)phenol (3) Base oil (8) + 0.55 wt % S-P + 0.4 wt % + Ester (12) (5 wt %)Yes anti-wear/extreme hindered pressure agent (2) phenol (3) Base oil(8) + 0.55 wt % S-P + 0.4 wt % + Ester (12) (10 wt %) Yesanti-wear/extreme hindered pressure agent (2) phenol (3) Base oil (8) +0.55 wt % S-P + 0.4 wt % + PIBSA (0.8 wt %) Yes anti-wear/extremehindered pressure agent (2) phenol (3) Base oil (8) + 0.55 wt % S-P +0.4 wt % + Ester (12) (3 wt %) + Yes anti-wear/extreme hindered PIBSA(0.16 wt %) pressure agent (2) phenol (3) Base oil (8) + 0.55 wt % S-P +0.4 wt % + Ester (12) (5 wt %) + No anti-wear/extreme hindered PIBSA(0.16 wt %) pressure agent (2) phenol (3) (1) Solvent refined base oil,about 88% saturates 150 SN oil. (2) Sulfur phosphorus extreme pressureagent CAS #83547-95-9 which is 60% sulfur-phosphorus component activeingredient (also contained C₄-C₈ diphenyl amine as balance of additive).The fully formulated lubricant has a phosphorus content of 120 ppm byweight, measured according to standard test ASTM D5185-97, attributableto the sulfur-phosphorus extreme pressure agent (which is the solephosphorus containing component contained in the formulation) (3) 100%active ingredient, CAS #125643-61-0. (4) PIBSA is polyisobutylenesuccinic anhydride having a polyisobutylene molecular weight of about950. (5) Hydrocracked 90 N, about 92% saturates. (6) 150 N FDA A gradewhite oil, 100% saturates. (7) Hydrocracked 150 N, about 99.9%saturates. (8) PAO-6, 100% saturates (9) base oil, a 50/50 mixture of150 N (88% saturates) and 400 N (about 78% saturates). (10) Formulationalso contained pour point depressant, antirust. (11) Esters tested weredi iso nonyl phthalate at 0.05 to 4 wt %; di iso tridecyl adipate at 0.1to 0.5 wt %; C₆—C₁₃ phthalate at 0.5 wt %. None were effective alone ateliminating crystal formation during the three month test period. (12)Di iso nonyl phthalate

What is claimed is:
 1. A lubricating oil of reduced crystal formationpotential, said formation potential attributable to the interaction ofsulfur phosphorus containing anti-wear/extreme pressure agents andhindered phenolic autioxidants, comprising a major amount of a base oilof lubricating viscosity and having a saturates content of 99 wt % ormore, and a minor amount of additives comprising a mixture ofsulfur-phosphorus containing anti-wear/extreme pressure additive, ahindered phenol antioxidant, a high molecular weight di- orpoly-carboxylic acid, anhydride or mixture thereof and an ester providedat least 0.0013 wt % high molecular weight carboxylic acid, anhydride ormixture thereof is present for each 1 ppm phosphorus attributable to thesulfur phosphorus containing anti-wear/extreme pressure agent, about0.033 wt % or more ester is present for each 1 ppm phosphorus and thecombination of high molecular weight acid, anhydride or mixture thereofand ester is employed in an ester to acid ratio of 25:1 by weight orhigher.
 2. The lubricating oil of claim 1 wherein the sulfur-phosphorusanti-wear/extreme pressure agent is in an amount sufficient to provideabout 2 ppm to 320 ppm phosphorus, the hindered phenol antioxidant is ata concentration of from about 0.01 to 2.0 wt % based on activeingredient and the high molecular weight di- or poly-carboxylic acid isat a concentration of in the range of about 0.0026 to 0.8 wt % based onactive ingredient, and the ester is at a concentration of about 0.042 wt% or more ester for each 1 ppm phosphorus.
 3. The lubricating oil ofclaim 2 wherein the sulfur-phosphorus containing anti-wear/extremepressure agent is in an amount sufficient to provide from 40 ppm to 200ppm phosphorus.
 4. The lubricating oil claim 3 wherein thesulfur-phosphorus containing anti-wear/extreme pressure agent is in anamount sufficient to provide from 80 ppm to 130 ppm phosphorus.
 5. Thelubricating oil of any preceding claim wherein the hindered phenol is ata concentration of about 0.1 to 1.0 wt % based on active ingredient. 6.The lubricating oil of claim 5 wherein the hindered phenol is at aconcentration of about 0.3 to 0.5 wt % based on active ingredient. 7.The lubricating oil of claim 6 wherein the high molecular weight di- orpoly-carboxylic acid, anhydride or mixture thereof is at a concentrationof about 0.08 to 0.4 wt % based on active ingredient.
 8. The lubricatingoil of claim 7 wherein the high molecular weight di- or poly-carboxylicacid, anhydride mixture thereof is a polyhydrocarbylene substitued di-or poly-carboxylic acid, anhydride or mixture thereof wherein thepolyhydrocarbylene group has a molecular weight in the range 300 to5,000.
 9. The lubricating oil of claim 8 wherein the high molecularweight di- or poly-carboxylic acid, anhydride or mixture thereof ispolyisobutylene succinic or maleic acid, anhydride or mixture thereofwherein the poly iso butylene has a molecular weight on the range 900 to1,000.
 10. A method for reducing crystal formation in lubricating oilcontaining a mixture of sulfur phosphorus anti-wear/extreme pressureagent and hindered phenols antioxidant wherein the sulfur-phosphorusanti-wear/extreme pressure agent interacts with the phenolic antioxidantto produce crystals, such method comprising adding to a major amount ofa base oil of lubricating viscosity having a saturates content 99 wt %or more, a minor amount of additives comprising a sulfur-phosphorouscontaining anti-wear/extreme pressure agent a hindered phenolantioxidant and a high molecular weight di- or poly-carboxylic acid,anhydride or mixture thereof and an ester provided at least 0.0013 wt %of the high molecular weight di- or poly-carboxylic acid, anhydride ormixture thereof is used for each 1 ppm phosphorus attributable to thesulfur-phosphorus containing anti-wear/extreme pressure agent, about0.033 wt % or more ester is present for each 1 ppm phosphorus and thecombination of high molecular weight di- or poly-carboxylic acid,anhydride or mixture thereof and ester is employed in an ester to acidratio of 25:1 by weight or higher.